Recent years have witnessed a growing trend towards the development and deployment of distributed generation (DG). This trend, in combination with new distributed generator technologies, has profoundly changed the traditional analysis, design, and control paradigm of distribution networks. The trend of integrating a wide variety of distributed resources into distribution networks also imposes great operational challenges; in particular, large-scale renewable energy penetration may cause overloading that occurs in distribution lines and transformers, voltage violation, and stability problems. The integration of various types of renewable resources also introduces another challenge on the capability of a distribution network to deliver powers from the locations of renewable resources to loads. The available delivery capability (ADC) of a distribution network of delivering powers from a collection of sources to a collection of sinks is defined as the maximum power that can be delivered over the existing amount for which there are no thermal overloads, voltage violations, and voltage collapse.
The concept of ADC in distribution networks is closely related to the concept of available transfer capability (ATC) in transmission networks. In 1996, the Federal Energy Regulatory Commission defined the term “available transfer capability” in transmission system to be posted in the Open Access Same-Time Information System to inform all energy market participants of the maximum power transfer capability for a distribution network. ATC has been used to guide power system operations for setting transfer limits on transmission corridors and key tie-lines for years. The concept of ATC can be extended into distribution networks to be “a measure of delivery capability in the physical distribution network for further delivery activity over and above already committed uses.”
The widespread use of distributed power generations in distribution networks imposes significant changes on operating conditions such as reverse power flow, voltage rise, increased fault levels, reduced power losses, island mode operation, harmonic problem and stability problem. System operators now face more new, unknown power flow patterns than ever before. At the same time, economic pressure on the electricity market and on grid operators, coupled with limited investment in new distribution networks, push distribution networks close to their stability limits. Hence, there is a need to monitor and calculate the ADC based on current operating conditions.